Field of Invention
The present invention relates to flyback power converter circuit, particularly to such a flyback power converter circuit capable of operating in a power regulation mode. The present invention also relates to a primary side controller circuit for use in the flyback power converter circuit and a method for controlling the flyback power converter circuit.
Description of Related Art
FIG. 1 shows a prior art flyback power converter circuit (flyback power converter circuit 1). The flyback power converter circuit 1 includes a transformer 10, a power switch N1, a primary side controller circuit 30 and a secondary side controller circuit 20. Please also refer to FIG. 2, wherein FIG. 2 shows waveforms corresponding to the prior art of FIG. 1. When the flyback power converter circuit 1 operates in a burst mode, when the auxiliary output voltage VDD1 (which is provided to the primary side controller circuit 30 as its power supply) is lower than a first voltage threshold VTH1, the primary side controller circuit 30 is triggered to enter into a power regulation mode, to control the level of the auxiliary output voltage VDD1 between the first voltage threshold VTH1 and the second voltage threshold VTH2.
The prior art shown in FIGS. 1 and 2 has a drawback that, when the power regulation mode is running, if the secondary side controller circuit 20 is required to enter into, e.g. a protection mode which needs to reboot the secondary side controller circuit 20, because the power regulation mode dominates the control of the auxiliary output voltage VDD1, the operation of the power switch N1 cannot be stopped by controlling the coupling device 40 to lower the feedback compensation signal COMP. Under such circumstance, the output voltage VDD2 (which is provided to the secondary side controller circuit 20 as its power supply) may stay at the level VHP, as shown in FIG. 2; in this case, the secondary side controller circuit 20 cannot be reboot. The above situation can very likely happen at certain levels of the output voltage VOUT. Therefore, in applications wherein the output voltage VOUT is adjustable (such as VBUS voltage compliant with the USB PD specification), such a problem occurs often.